John III may refer to:

People

  • Pope John II (III) of Alexandria, Patriarch of Alexandria from 505 to 516
  • John III (bishop of Jerusalem) in 516–524
  • Pope John III, Pope from 561 to his death in 574
  • John Scholasticus, Patriarch of Constantinople from 565 to his death in 577
  • Pope John III of Alexandria, Coptic Pope from 680 to 689
  • John III Rizocopo, Exarch of Ravenna from 710 to 711
  • John III of the Sedre, Syriac Orthodox Patriarch of Antioch from 631 to his death in 648
  • John III of Naples, Duke from 928 to his death in 968
  • John III of Gaeta, Duke from 984 to his death in 1008
  • John III of Amalfi, Duke in 1073
  • John III Doukas Vatatzes (c. 1192 – 1254), Emperor of Nicaea
  • John III Comyn of Badenoch (died 1306)
  • John III, Duke of Brittany (1286–1341)
  • John III, Duke of Brabant (1300–1355)
  • John III Megas Komnenos (c. 1321 – 1362), Emperor of Trebizond
  • John III of Montferrat (c. 1362 – 1381)
  • John III, Burgrave of Nuremberg (c. 1369 – 1420)
  • John III, Count of Auvergne (1467–1501)
  • Ivan III of Russia (1440–1505), Grand Duke of Russia since 1462
  • John III of Navarre (1469–1516)
  • John III Crispo, Duke of the Archipelago (1480–1494)
  • John III, Duke of Cleves (1490–1539)
  • John III of Portugal (1502–1557), King of Portugal and of the Algarves
  • John III of Sweden (1537–1592)
  • John III Sobieski (1629–1696), King of Poland and Grand Duke of Lithuania
  • Yohannes III of Ethiopia (c. 1824 – c. 1873), Emperor several times between 1840 and 1851
  • Prince Jean, Duke of Guise, pretended to the title John III, King of the French, 1926–1940
  • Infante Juan, Count of Barcelona, pretended to the title Juan III, King of Spain, 1941–1977
  • Juan de Borbón y Braganza, Carlist pretender to the title, Juan III, King of Spain, 1861-1868 and Legitimist pretender to title, Jean III, King of France.
  • John Ernest III, Duke of Saxe-Weimar (1664–1707)
  • John Frederick III, Duke of Saxony (1538–1565)
  • John William III, Duke of Saxe-Eisenach (1666–1729)
  • Jean, Grand Duke of Luxembourg, the 3rd ruler of Luxembourg of that name

Biblical

  • John 3, the third chapter of the Gospel of John
  • Third Epistle of John or 3 John
  • Ioannes III (disambiguation)